Many passenger vehicles are equipped with supplemental inflatable restraints, i.e., air bags, for vehicle occupants. Many of these air-bag-equipped vehicles also include cover assemblies that conceal the supplemental restraints. For primarily aesthetic reasons, it is desirable for such cover assemblies to include continuously formed outer skins or covers that provide no outward indication that an air bag assembly is concealed beneath or behind.
When an air bag inflates in response to a vehicle collision, a continuously-formed outer skin must tear open through a wide range of temperatures to allow the inflating bag to expand into the passenger compartment in a predictable manner.
One such method of controlling outer skin tearing is to create a weakened tear seam by weakening a linear portion of the outer skin so that tearing will occur along that weakened line when the air bag inflates. Weakening is sometimes accomplished by such means as perforating, cutting or melting the outer skin prior to assembling the cover assembly. For example, U.S. Pat. No. 5,131,678, assigned to the assignee of the present application, discloses an air bag cover assembly that includes a weakened tear-seam formed in the outer surface of an outer skin prior to assembly by cutting. The '678 patent does not, however, provide for concealment of the weakened tear-seam from passenger compartment occupants.
Another method of controlling outer-skin tearing is to use one or more pressure-assist members such as cutters or tear edges. For example, U.S. Pat. No. 4,097,064 discloses a cover assembly with a rigid applique in the form of a semi-rigid pad that is supported in a layered disposition over an outer skin. A cutter is mounted on the inner surface of the semi-rigid pad with a sharp cutting edge extended inward toward the outer skin. Air bag inflation forces the outer skin outward into contact with the inwardly-directed cutter, cutting the outer skin and releasing the inflating air bag. The position of the cutter on the inner surface of the pad also serves to conceal the cutter from vehicle occupants.
The prior art also includes an air bag cover assembly that employs both outer-skin weakening and a tear edge positioned along the weakened tear seam. U.S. Pat. No. 5,375,875 discloses a cover assembly with a weakened tear-seam formed in the inner surface of an outer skin, and a tear edge on a cutter panel that swings outwardly under the force of air bag inflation to cut the outer skin along the weakened tear-seam. The weakened tear seam is concealed from passenger compartment occupants by positioning it on the inner surface of the outer skin.
It would be desirable to provide an air bag cover assembly that controls the tearing of a continuously-formed outer skin by weakening a tear seam in the outer surface of the skin while concealing the weakened seam from passenger compartment occupants.